<!DOCTYPE html>
<html>
  <head>
    <meta charset="utf-8" lang="zh" />
    <title>第一个html</title>
  </head>
  <body>
    <script>
      var a = 123;
      document.write("Hello, world! " + a);
      
    </script>
    <h1>一级标题</h1>
    <h2>二级标题</h2>
    <h3>三级标题</h3>
    <h4>四级标题</h4>
    <h5>五级标题</h5>
    <h6>六级标题</h6>
    <p>这是一个段落</p>
    这是第一个html aaa bbb ccc
    <ol>
      <li>aaaa</li>
      <li>bbbb</li>
      <li>cccc</li>
      <li>dddd</li>
    </ol>
    <div>
      <iframe src="https://www.baidu.com" frameborder="1" width="500" height="500"></iframe>
    </div>
  </body>
</html>
